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Many governments have set a goal for limiting climate change: two degrees by the end of the century, and no more. However, most projections show we're lagging badly. Unless we accelerate a transition to renewables and nuclear, we're going to shoot right past that 2°C limit. But even as the hand-wringing about missed targets and bad trajectories has increased, it's been relatively rare to see a detailed analysis of the potential consequence. The World Bank has now stepped into that breach.

In a report released today, the World Bank analyzed the consequences of allowing temperatures to reach 4°C above pre-industrial levels by the end of the century. Even the well understood problems—up to a meter of sea level rise, winter months that are warmer than our current summers—sound pretty ugly. The report also notes the possibility of tipping points and synergies make some of the impacts much harder to predict.

The report itself is a collaboration between the Bank's Global Expert Team for Climate Change Adaptation and the Potsdam Institute for Climate Impact Research and Climate Analytics. In addition to taking a different perspective on the problem of climate change, the report comes at a valuable time. It's been five years since the release of the fourth Assessment Report from the Intergovernmental Panel on Climate Change; the fifth isn't due until late next year.

So, what are the chances of adding an extra 4°C by the end of the century? The report estimates that, even if all countries are able to meet their current emissions pledges, there's still a 20 percent chance we'll hit 4°C by the end of the century. The longer we wait to meet those pledges, the harder it will be in part because it means we've already built fossil fuel infrastructure that has a life span of decades.

What does a world that much warmer look like? To give a sense of how hard it is to imagine, the report notes some points in the last glacial period were only 4.5°colder than present temperatures—and there were ice sheets covering a lot of the Northern Hemisphere. We've already hit levels of CO2 in the atmosphere that haven't been seen in over 15 million years. To reach 4°C, they'd have to roughly double again. And these changes would take place at a pace that probably has few geological precedents.

So, even the report's authors admit that predications are a challenge. Still, they do their best to try to paint a picture, and boy, is it grim.

Sea level would rise by a half-meter or more, putting lots of coastal infrastructure and plenty of people at risk. The typical summer temperatures would be the equivalent of our worst heat waves. In fact, the specifically note that normal temperatures in Russia would be similar to those of its recent heat wave, which killed 55,000 people and caused massive property damage. Meanwhile, the baseline winter temperatures would be equivalent to our current summers in most areas. Temperatures over land will rise faster than they do over the ocean, and some regions will be especially hard hit. The authors predict that typical temperatures in the Mediterranean will be up by roughly 9°C.

Rainfall patterns would shift dramatically, with some river basins seeing a reduction of over 20 percent in water while others get additional rainfall. That will add to the stresses on agriculture, where many crops will already be pushing up against temperature limits in current growth zones. Meanwhile, the level of ocean acidification driven by our emissions may stop coral reef growth as soon as the 2030s. Acidification may also begin reducing reefs by the end of the century.

All of that sounds pretty awful, but that's not the end of it. Even if atmospheric greenhouse gas levels were stabilized by the end of the century, it would take our planet time to reach a new equilibrium. Temperatures would continue to rise, with the global mean reaching 6° over pre-industrial levels. Sea levels would continue to rise, reaching somewhere between 1.5m and 5m above present levels. That later figure is higher than the storm surge that swept into Atlantic City, New Jersey.

In addition, the report raises the spectre of nonlinear events, commonly called tipping points, where a current equilibrium is shifted to a new state entirely. It points out there might be synergistic effects that could make a combination of tolerable impacts difficult to manage. For example, reduced rainfall, elevated temperatures, and saltwater intrusion from rising ocean levels could all have a negative impact on agriculture. At the same time, loss of port facilities to sea level rise could make importing crops from elsewhere a challenge.

If all of this is a bit shocking, then the report achieves its desired effect. "It is my hope that this report shocks us into action," said World Bank President Jim Yong Kim. "Even for those of us already committed to fighting climate change, I hope it causes us to work with much more urgency." He said that the Bank's goal of economic development and poverty reduction could be met without pushing against planned emissions limits.

This report won't win over any converts. The projections for change are based on the output of climate models, and people who don't trust them won't suddenly start doing so. Critics of action on climate change will undoubtedly pick over the details. The report notes research had indicated droughts were increasing, but a reanalysis of data that's only a week old suggests those estimates were off. This doesn't mean every aspect of the report is suspect, but expect it to be treated that way.

Ultimately, the report could be a valuable wake up call for those who are willing to accept many of the conclusions of climate scientists. It's easy to accept that progress towards emissions reduction will be irregular, but the World Bank is clearly hoping to keep that acceptance from becoming complacency.